Gaseous microwave switching tube apparatus, said tube including closely packed solid ceramic spheres



E J. OQOK 3,332,4G GASEOUS MICROWAVE SWITCH ING TUBE APPARATUS, SAID TUBE INCLUDING CLOSELY PACKED SOLID CERAMI C SPHERES Filed May 22, 1964 2 Sheets-$heet l FH SG (ALUMJNA cammac ALUMINA v CERAMIC W INVENTOR.

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T A R A P P A E B U T GASEOUS MICROWAVE SWITCHI INCLUDING CLOSELY PACKED SOLID CERA y 22, 1964 2 Sheets-Sheet Filed Ma RECEW INVENTOR EDWARD J. COOK United States Patent 3,332,040 GASEOUS MICROWAVE SWITCHING TUBE AP- PARATUS, SAID TUBE INCLUDING CLOSELY PACKED SOLID CERAMIC SPHERES Edward J. Cook, South Hamilton, Mass., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed May 22, 1964, Ser. No. 369,548 8 (Ilaims. (Cl. 333-13) The present invention relates in general to gaseous microwave switching devices and more particularly to an improved gaseous switching device having its active region filled with a solid dielectric materal thoroughly permeated with gas filled voids thereby providing increased operating life and decreased recovery time. Such improved switching devices are useful, for example, in microwave receiver protectors of the T.R. and pre-T.R. type.

Heretofore, gas filled microwave switching devices have been built which had an active region of the gas fill stuffed with quartz fibers to a degree having a solid dielectric filling factor substantially less than 50% to decrease the recovery time, i.e., the time for sufiicient deionization of the gas to take place to reduce the insertion loss to a point only 3 db above the cold insertion loss. However, use of quartz fibers did not reduce the recovery time sufficiently and, therefore, other measures, such as use of an attachment gas in a folded cylinder, were employed to reduce the recovery time to on the order of 20 seconds. The problem with use of an attachment gas was that the attachment gas increased the power absorbed by the discharge, commonly called arc-loss, resulting in over heating of the switching device which rapidly depleted the gas fill and rendered the gas switching device inoperative after only 100 200 hours of operation at high power levels of a few megawatts peak power and a few kilowatts average power. Operating life could be increased by using pure high mobility noble gas fill such as argon and deleting the attachment gas, but, then, the recovery time was increased to in the order of 100s of microseconds, too long for many applications. Prior efforts were made to decrease the recovery time of the pure noble gas filled folded cylinder by reducing the annular gap width between adjacent walls of the folded cylinder to decrease the gas diffusion time to the walls of the cylinders. However, it was found that while reduction of this gap width did decrease the recovery time it also undesirably increased the firing threshold and leakage power of the switch tubes. Thus, it was found 0.01 "-0.020 was the lower practical gap width limit for L band switches which yielded recovery times in excess of 100,1 seconds for pure gas fill optimum folded cylinder geometries.

In a preferred embodiment of the present invention, the active gaseous region of a gaseous microwave switching tube is loaded with closely packed spheres of high dielectric material such as alumina ceramic. The voids inbetween the packed spheres are filled with the high mobility noble gas. The spheres provide close recombination surfaces for neutralizing the ionized gas and reduce the recovery time by an order of magnitude for pure gas fill switches.

The principal object of the present invention is to provide an improved gaseous microwave switching apparatus.

One feature of the present invention is the provision of loading a preponderance by volume of the active region of a gaseous switching device with a solid dielectric material ceramic spheres with the voids between the spheres filled with the active switching gas medium whereby recovery time is substantially reduced.

Another feature of the present invention is the same as the preceding feature wherein the spheres are alumina ceramic.

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Other features and advantages of the prsent invntion will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal sectional view of a gaseous discharge microwave switch element embodying features of the present invention,

FIG. 1 (a) is a schematic drawing showing the effect of the closely packed dielectric pellets on the RR electric fields,

FIG. 2 is a longitudinal sectional view of a folded cylinder type gaseous discharge microwave switch element embodying features of the present invention,

FIG. 3 is a transverse sectional view of a receiver protector tube embodying a switching element of the present invention,

FIG. 4 is a longitudinal section of the structure of FIG. 3 taken along line 44 in the direction of the arrows,

FIG. 5 is a schematic circuit diagram partly in block diagram form of a microwave duplexer circuit employing switching elements of the present invention, and

FIG. 6 is a transverse sectional View of the duplexer switching portion of the circuit of FIG. 5 delineated by line 66, and

FIG. 7 is a longitudinal sectional view of the structure of FIG. 6 taken along line 77 in the direction of the arrows.

Referring now to FIG. 1, there is shown a gaseous microwave switching element embodying features of the present invention. More specifically, a hollow cylindrical vial 1 as of fused quartz having an outside diameter of 0.250 and a wall thickness of 0.020 is filled with a multitude of closely packed solid refractory dielectric pellets 2 as of, for example, 0.015" in diameter. The pellets 2 should have a dielectric constant greater than 2 and preferably as high as possible. In a preferred embodiment, the pellets 2 are formed by alumina ceramic spheres having a dielectric constant of 9. Also, it is considered desirable that the dielectric material have as high a secondary emission ratio as possible consistent with the other desirable characteristics in order to facilitate breakdown of the gas during the switching phase of operation, more fully described below. Before evacuation, quartz Wool 3 is stuffed into the vial 1 to hold the spheres in place during evacuation and to prevent their being drawn into the vacuum pump with the outflowing gases.

The pellet packed vial 1 is evacuated and then filled to a reduced pressure with a suitable inert ionizable switching gaseous atmosphere preferably having high mobility consistent with the ability to be stored within the vial 1 for long periods of time. Such low mobility inert gaseous atmospheres includes the low atomic weight noble gases such as argon, helium and neon. However, helium is excluded for use with quartz walled vials since helium will diffuse through the walls of the vial and be lost. In a preferred embodiment of the present invention, the vial 1 is filled with pure argon to a pressure of 20-100 mm. Hg. After gas filling, the vial 1 is sealed off as by heat sealing.

In operation, an intense microwave electric field in a wave transmission structure is applied to the vial 1. The gas fill which permeates the voids between the pellets is ionized by the microwave energy thereby presenting a conductive short circuit across the transmission system and reflecting the power incident thereon, thereby switching the transmission structure from a conducting to a non-conducting state. The function of the high dielectric constant pellets is to decrease the effective wall spacing to enhance recombination .and at the same time prevent a substantial increase in the firing power threshold. The firing power threshold is held at a low level by increasing the electric field intensity in the gaseous regions inbetween adjacent pellets and increasing secondary emission due to the high secondary emission ratio of the alumina ceramic pellets 2. The sphere filled normal cylinder of FIG. 1 provides an operating life of 5000 hours as com- 4 the same mode of operation as previously described with regard to the normal cylinderof FIG. 1.

Referring now to FIGS. 3 and 4, there is shown a typical receiver protector device using a gas switching device pared to a prior art operating life of 200 to 500 hours in 5 according to, the present invention. More specifically, a comparable devices using an attachment gas constituent. hollow rectangular waveguide 9, provided withconven- The effectively increase in the electric field strength tional coupling flanges 11 at its ends, is partitioned into a is obtained due to a voltage dividing and concentrating gas tight chamber 12 defined by the internal region of effect illustrated in FIG. 1(a). Between tw-o arbitrary space between a pair of resonant R.F. gas tight window R.F. equipotential lines V and V there will be a given assemblies 13, and14, respectively. Chamber 12 is filled R.F. voltage. The E field or voltage-drop per unit distance with an inert ionizable gas atmosphere at reduced pressure is inversely proportional to the dielectric constant of the such as argon. Two pairs of mutually opposed conical medium in which the field exists. Therefore, the field metallic electrodes and 16, respectively, protrude into intensity in the gas fill is 9 times higher than in the alumthe chamber from the top and bottom broad walls of'the in-a ceramic dielectric spheres. Therefore, for that part of 15 waveguide 9 and are each centered in the guide between the medium between. the equipotential planes occupied a pair of inductive iris vanes 17.. by the high dielectric constant material (solid alumina The resonant windows 13 and 14 are dimensioned to ceramic) there will be much less voltage drop, whereas provide a'high degree of wave energy coupling therefor thoseportions of the medium, having low dielectric through and dimensioned to have a low Q of approxiconstant (-gas filled voids have a dielectric constant of l) mately 1.0. The conical electrodes 15 and 16 are each there will be much more voltage drop. Furthermore, since resonated withi their accompanying inductive iris 17 to the voids are much smaller in length taken along the elecform low Q resonant irises 18 and 19. The resonant irises tric field lines than the field path length through the solid 18 and 19 are each 90 electrical phase degrees apart in dielectric and because of the small point contacts bethe axial direction of the waveguide and are also 90 electween adjacent spheres which prevent shunting the electrical phase degrees apart from their closest window astric field around the voids there is a very substantial semblies 13 and 14, respectively, to thereby form a combuild-up of'electric field in the gas filled voids to initiate posite broad passband wave transmission circuit with its a gaseous discharge. Moreover, the high secondary emiscenter frequency selected for the center frequency of the 51011 ratio of the alumina ceramic surface helps to initiate transmitter for which the device is to protect the receiver. the discharge due to secondary electron current. The receiver protector is connected in the transmission It has been found that the solid dielectric pellet filled circuit such that the window assembly 13 faces the transgas switching element has greatly enhanced recovery mitter and window 14 faces the receiver. times as compared to prior quartz wool filled elements Window assembly 13 includes a low Q multiple transoperated under comparable conditions. Also, the thresverse iris metallic window frame 21 as of Kovar sealed hold firing power is substantially reduced as compared to across the guide 9. The multiple irises of the frame 21 are prior pure noble .gas quartz fiber filled gas switching sealed over in a gas tight manner by a glass member 22 device. There is a table, below, which compares the. pellet melted over the apertured frame 21. A gas switching plus pure noble gas filled cylinder and folded cylinder device according to FIG. 1 is-disposed immediately in devices with prior quartz wood filled devices. front of the windowframe 21. In a preferred embodiment,

TABLE- Type Gas Fill Loading Material Recovery Firing Threshold Peak Freq. Avg. Isolation Time, 4880. Power Band Power db Folded cylinder Pure Argon A1203 pellets 7 3 kw. consistent... 31 Normal cylinder .do ..do 3-4 20 Folded cylinder do Quartz wool. 31 Normal cylinder Argon plus ammonia" do 5-6 20 Folded cylinder Pure Argon None.- 100 31 Referring now to FIG. 2, there is shown the folded the switching device is centrally disposed of the guide 9 cylinder gas switching tube geometry employing the solid and extends across the guide from one broad wall to the pellet fill feature of the present invention. The folded other. The pellet-and gas filled vial 1 is held in position cylinder vial 4 is constructed of a pair of coaxially nested by, and coaxially mounted within, a pair of mutually oprefractory dielectric cylinders 5 as of fused quartz each posed ,coaxially aligned metallic sleeves 23. A pair of incylinder having one closed end 6 and the cylinders being ductive iris plates 24 transversely flank the vial 1 to form sealed together at their open ends 7. The sealed cylinders the composite low Q resonant window assembly 13. define an elongated annular chamber 8 therebetween A conventional shutter protector assembly 26 of. the which is. filled with closely packed refractory pellet 2 as type described in US. Patent 2,734,171 is coaxially disabove described. Quartz wool 3 is packed across the enposed of the first pair of resonant conical elements 15. A larged end of the annular chamber 8 to prevent loss of the conventional keep alive electrode assembly 27 of the type pellets 2v duringevacuation, as above described. In a described in U.S..Patent 2,680,207 is coaxially disposed typical example, the annular chamber 8 has a gap width of the second pair of resonant conical electrodes16. of 0.060" and a cylinderwall thickness of 0.070 and a In operation, transmitter power P, traveling from left length of 18". The pellets are alumina ceramic spheres to right in FIG. 4, is incident upon the receiver protector of 0.015 diameter. circuit. Power traverses the circuit until it hits the pair One advantage of the folded cylindrical geometry over of electrodes 16 which includes the keep alive electrode the normal cylindrical geometry of FIG. 1 is that the, assembly 27. The resonant iris 19 breaks down and forms folded cylinder, when positioned across an iris or window, an arc across the guide 9. The are reflects the transmitter as is customary, introduces less capacitive loading than a power back toward the transmitter. The reflected power normal cylinder filled with ceramic pellets 2 and, the-replus .the incident power produces a gas breakdown or fore, less detuning of the iris or window is obtained with plasma discharge in the pellet filled vial 1. In this manner, the pellet filled folded cylinder. The folded cylindrical the power absorbed by the switching plasma discharge geometry is often used in pre-T.R; tubes and duplexers. mechanism is removed from the back side of the window The folded cylinder pellet filled pure noble gas tube has frame 21 and concentrated, instead, in the vial 1 which is preferably disposed in a gas filled and high pressurized section of guide 9. Upon termination of the transmitted pulse of wave energy, the plasma discharges within the vial 1 and chamber 12 are quickly extinguished to permit passage therethrough of wave energy received from the antenna and passing from left to right through the receiver protector circuit to the receiver.

Referring now to FIGS. 6 and 7, there is shown a typical pre-T.R. receiver protector circuit employing folded cylinder pellet filled vials 4 of the present invention as above described with regard to FIG. 2. The particular type of installation shown in FIG. 5 is a microwave duplexer circuit 31 which comprises a 4-port waveguide network. A transmitter 32 is connected to one port 33. A single antenna 34 which serves to both transmit and receive signals is connected to a second port 35. A pair of parallel waveguides 36 are connected to the antenna 34 and transmitter 32 via a conventional short slot hybrid coupler 37.

An energy absorbing termination 38 is connected to a third port 39. A receiver protector circuit 41, as shown in FIGS. 3 and 4, is connected to a fourth port 42. A receiver 43 is connected to the receiver protector circuit 41. A conventional short slot hybrid coupler 44 couples ports 39 and 42 to the parallel waveguides 36.

A dual pre-T.R. assembly 45, indicated by the dotted lines of FIG. 5, is connected midway of the parallel waveguide branches 36. The dual pre-T.R. assembly 45 includes a pair of thick walled metallic iris plates 46 as of 2" thick copper transversely mounted of and across the guides 36. A pair of elongated irises 47, parallel directed of the broad walls of the guides 36, are cut through the plates 46 for passage of wave energy therethrough. A pair of transverse bores 48 as of 1" in diameter pass through the center of, and in the plane of, the plates in a direction parallel to the broad walls of the guide 36. The bores have their center lines in substantial alignment with the axial center lines of the elongated irises 47. A pair of pellet and gas filled folded cylinder vials 4, as above described with regard to FIG. 2, are coaxially disposed of the bores 48.

In operation, high power wave energy supplied from the transmitter 32 and applied to the duplexer 31 at port 33 fires the folded cylinders 4 on the dual pre-T.R. assembly 45 causing the transmitted power to be reflected out of the duplexer 31 via port 35 to the antenna 34. The small leakage power, passed by the dual T.R. 45, passes out via port 42 and fires the receiver protector 41 thereby protecting the receiver 43. Upon termination of the transmitted pulse, the folded cylinders 4 and receiver protector 41 recover their non-ionized state and permit signals received via antenna 34 to be transmitted to the receiver 43. The common folded cylinder vials 4 which extend through both waveguides 36 assure that both waveguides 36 are switched simultaneously from the conductive to the nonconductive state thereby assuring proper operation of the duplexer circuit 31. The folded cylinder vials 4 operated 400 hours without signs of degradation of performance, whereas the prior vials, using an attachment gas fill, had an operating life of only 100 to 200 hours. Moreover, the firing power threshold was stabilized at 3 kilowatts, whereas the prior firing threshold varied between 3 and kilowatts.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What I claim is:

1. A gaseous microwave switching tube apparatus including, means forming a dielectric electrodeless envelope containing no electrodes therewithin, said envelope including a fill of closely packed solid dielectric ceramic spheres having a dielectric constant greater than 6 and a secondary electron emission ratio at least equal to that of alumina ceramic, said fill being thoroughly permeated with voids of generally uniform size defined by the spaces inbetween the packed ceramic spheres, said ceramic spheres occupying a preponderance by volume of the active region of said gaseous switching apparatus, and

said voids being filled with a gaseous switching medium, whereby recovery time is substantially reduced.

2. The apparatus according to claim 1 wherein said closely packed ceramic spheres are alumina ceramic.

3. The apparatus according to claim 1 wherein said dielectric envelope is rnade of quartz.

4. The apparatus according to claim 1 wherein said dielectric envelope is of the folded cylinder configuration to define an annular gaseous switching chamber loaded with said ceramic spheres.

5. A microwave switching apparatus including, means forming a microwave transmission network for transmitting microwave energy therethrough, means forming a gaseous switching device disposed in said microwave transmission network for switching said network from a conductive to a nonconductive state, said gaseous switching means including an electrodeless dielectric vial, said vial being loaded with a multitude of close-1y packed dielectric ceramic spheres having a dielectric constant greater than 6 and a secondary electron emission ratio at least equal to that of alumina forming an active switching region of space having a preponderance by volume of solid dielectric material and being thoroughly permeated with a multitude of voids of generally uniform size in the regions of space inbetween said spheres, said voids being filled with an active switching gaseous medium which is rendered conductive upon the application of microwave power thereto of sufficient amplitude, said conductive gaseous medium serving to switch said transmission network from a conductive to a substantially nonconductive state, whereby the recovery time is substantially reduced.

6. The apparatus according to claim 5 wherein said gaseous switching medium is a pure noble gas.

7. The apparatus according to claim 5 wherein said dielectric ceramic spheres are alumina ceramic and said gas fill is argon.

8. The apparatus according to claim 5 wherein said vial is of the folded cylinder configuration defining an annular chamber filled with said closely packed ceramic spheres, and said transmission system includes a rectangular waveguide having pairs of broad and narrow walls and a coupling iris formed therein, said coupling iris being elongated in a direction parallel to the broad walls of said rectangular waveguide, and said folded cylinder vial being disposed immediately adjacent said coupling iris for shorting same upon application of said microwave power of sufiicient amplitude.

References Cited UNITED STATES PATENTS 1,851,532 3/1932l Vollrath 313-203 2,496,865 2 1950 Fiske 313-203 X 3,209,285 9/ 1965 Manwarren et al 31313 FOREIGN PATENTS 1,158,186 11/1963 Germany.

377,23 8 7/ 1932 Great Britain. 600,889 4/ 1948 Great Britain.

OTHER REFERENCES Reference Data for Radio Engineers, 4th ed., ITT, 1956, p. 64 relied on.

Bruining: Secondary Electron Emission, Permagon Press Ltd., London, 1954, p. 53 relied on.

HERMAN KARL SAALBACH, Primary Examiner.

P. L. GENSLER, Assistant Examiner. 

1. A GASEOUS MICROWAVE SWITCHING TUBE APPARATUS INCLUDING, MEANS FORMING A DIELECTRIC ELECTRODELESS ENVELOPE CONTAINING NO ELECTRODES THEREWITHIN, SAID ENVELOPE INCLUDING A FILL OF CLOSELY PACKED SOLID DIELECTRIC CERAMIC SPHERES HAVING A DIELECTRIC CONSTANT GREATER THAN 6 AND A SECONDARY ELECTRON EMISSION RATIO AT LEAST EQUAL TO THAT OF ALUMINA CERAMIC, SAID FILL BEING THOROUGHLY PERMEATED WITH VOIDS OF GENERALLY UNIFORM SIZE DEFINED BY THE SPACES INBETWEEN THE ACKED CERAMIC SPHERES, SAID CERAMIC SPHERES OCCUPYING A PREPONDERANCE BY VOLUME OF THE ACTIVE REGION OF SAID GASEOUS SWITCHING APPARATUS, AND SAID VOIDS BEING FILLED WITH A GASEOUS SWITCHING MEDIUM, WHEREBY RECOVERY TIME IS SUBSTANTIALLY REDUCED. 